Conventionally, as described in the following Patent Document 1, there is known a device which irradiates a tabular scintillator with X-rays emitted from an X-ray source and transmitted through an imaging object, detects visible light (scintillation light) generated in the scintillator by solid-state photodetectors laminated on both surfaces of the scintillator, and superimposes image signals output from the respective solid-state photodetectors on each other to acquire a radiation image. In this device, photodetecting elements are coupled to an X-ray incidence surface of the scintillator and its back surface, and the detection efficiency for visible light is enhanced by detecting visible light in each of the photodetecting element on the incidence surface side and the photodetecting element on the back surface side.
Also, as described in the following Patent Document 2, there is known a device which, by use of two scintillators overlaid with each other and one detector, detects scintillation light emitted from the scintillator on an incidence surface side by one surface of the detector, and detects scintillation light emitted from the scintillator on the opposite side by the other surface of the detector. In this device, images are formed with two types of different wavelengths on the respective surfaces of the detector.